sep 2.0 mapping for grid control enabled inverters the new california (ca) rule 21 interconnection...
TRANSCRIPT
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ACKNOWLEDGMENTS
The following organization prepared this report:
Electric Power Research Institute (EPRI)
3420 Hillview Avenue
Palo Alto, California 94304-1338
Principal Investigator
G. Aumaugher
This report describes research sponsored by EPRI.
Any opinions, findings, and conclusions or recommendations expressed in this material are those
of the author(s) and do not necessarily reflect the views of the CPUC, Itron, Inc. or the CSI
RD&D Program.
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ABSTRACT
This technical update addresses how Smart Energy Profile 2.0 (SEP2) can be used to support
grid control enabled inverters. This implementation is intended for use in the Standard
Communication Interface and Certification Test Program project.
This project consists of the development and demonstration of advanced inverters with
standardized functionality and an open communication interface that can meet the requirements
of the new California (CA) Rule 21 interconnection guideline. The communication interface will
utilize the IEC standard information model, the SunSpec protocol, and the CEA-2045 modular
interface to enable off-the-shelf inverters to be mass produced, and compatible with SCADA,
AMI, or any other system.
This report is intended for the member utilities involved in the Standard Communication
Interface and Certification Test Program project.
Keywords Smart Inverters
Distributed Energy Resources
DER
SEP 2.0
SEP2
California (CA) Rule 21
vii
CONTENTS
1 INTRODUCTION ..................................................................................................................1-1
Overview ............................................................................................................................1-1
Functions to Be Supported ...........................................................................................1-1
2 INDIVIDUAL FUNCTION MAPPING .....................................................................................2-1
Volt-VAR Curve Download .................................................................................................2-1
Frequency-Watt Curve Download .......................................................................................2-2
Volt-Watt Curve Download .................................................................................................2-3
DER Curve Enable/Disable ................................................................................................2-5
Ramp Rate Download ........................................................................................................2-5
Fixed Power Factor ............................................................................................................2-5
Limit Maximum Real Power ................................................................................................2-6
Connect/Disconnect ...........................................................................................................2-8
Upload Inverter Alarms and Status .....................................................................................2-8
3 IDENTIFIED ISSUES ............................................................................................................3-1
One Event Active per Program ...........................................................................................3-1
4 REFERENCES .....................................................................................................................4-1
ix
LIST OF FIGURES
Figure 2-1 Simple Volt-VAR curve............................................................................................2-1 Figure 2-2 Example Frequency-Watt curve with hysteresis ......................................................2-2 Figure 2-3 Example Volt-Watt curve .........................................................................................2-4 Figure 2-4 Limit Maximum Real Power ....................................................................................2-7 Figure 2-5 DER Connect/Disconnect switch .............................................................................2-8
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LIST OF TABLES
Table 2-1 Subset of the Volt-VAR curve parameters ................................................................2-2 Table 2-2 Subset of the Frequency-Watt curve parameters .....................................................2-3 Table 2-3 Subset of the Volt-Watt curve parameters ................................................................2-4 Table 2-4 Subset of the DER curve enable/disable event structure ..........................................2-5 Table 2-5 Subset of the DERControl fixed power factor event structure ...................................2-6 Table 2-6 Subset of the DERControl limit maximum real power event structure .......................2-7
1-1
1 INTRODUCTION
Overview
The Standard Communication Interface and Certification Test Program project consists of the
development and demonstration of advanced inverters with standardized functionality and an
open communication interface that can meet the requirements of the new California (CA) Rule
21 interconnection guideline. The communication interface will utilize the IEC standard
information model, the SunSpec protocol, and the CEA-2045 modular interface to enable off-
the-shelf inverters to be mass produced, and compatible with SCADA, AMI, or any other
system.
The project will also develop a certification test program, including the test procedures, software,
and facilities needed to validate that new inverter designs function and communicate per the
standards. A certification process is a must-have because standards alone are not sufficient to
produce interoperability. The certification process will be based on the California Rule 21
requirements, and will include testing of both the power and communication interfaces of the
inverter. In this way, the inverters could be fielded immediately, with confidence that they could
be successfully integrated with control systems at a later time, if and when needed.
One of the communication protocols being demonstrated in this project is SEP2. This protocol
was designed to support smart inverter functions required to take advantage of new capabilities,
some of which are being demonstrated in this project.
Functions to Be Supported
The following functions will be supported using SEP2:
Download of Volt-VAR mode with Watt-Priority curves
Download of Frequency-Watt mode curves
Download of Volt-Watt mode curves
Enable/disable specific Volt-VAR/Frequency-Watt/Volt-Watt curves
Download of ramp rates for specific functions
Fixed Power Factor settings
Report inverter alarm status
Report inverter instantaneous power, power factor, connection status, and totalized real
power output
SEP2 supports most of the required distributed energy resources (DER) functionality without
modification or hijacking of other functions. The only identified exception to this is alarm
reporting.
1-2
Some of the information on the functions to be supported was drawn from the publically
available technical update, Common Functions for Smart Inverters, Version 3, EPRI product ID
3002002233. It is assumed that the parameters for Rule 21 functions to be supported will be
similar.
2-1
2 INDIVIDUAL FUNCTION MAPPING
This chapter provides details on how the individual DER functions to be supported for this field
demonstration are mapped to the SEP 2.0 functions. Four models will be used to support the
required functions: DERCurve, DERControl, DERStatus, and meter mirroring.
1) DERCurve will be used to download the three required curve types to the inverter.
2) DERControl will be used to limit the inverter power output, enable or disable DER
curves, and connect/disconnect.
3) DERStatus and Meter mirroring will support the status provided to the SEP 2.0 server.
SEP 2.0 uses programs to contain function sets, such as DERControl. Per the specification, a
program cannot have more than one DER event active at one time. Since many of the DER
functions to be implemented are meant to coexist with other functions, a separate program must
be created for each of these functions. Only functions that are mutually exclusive may reside in
the same program.
Each function will be discussed in detail in the following sections.
Volt-VAR Curve Download
The Volt-VAR curves loaded into the inverter define how dynamic reactive power is injected
through autonomous responses to local voltage measurements. The SEP2 client will request a
download of a DER Curve from the SEP2 server. Multiple curves may be downloaded and are
identified by their mRID value.
SEP2 Function set: DERCurve / DERCurveType: 0 - Volt-VAr Curve Mode: opModVoltVAr
A simple Volt-VAR curve is shown in Figure 2-1.
Figure 2-1 Simple Volt-VAR curve
2-2
Some of the primary elements of interest in this function are shown inError! Reference source
not found. See the SEP 2.0 specification for full details.
Table 2-1 Subset of the Volt-VAR curve parameters
Structure Description
DERCurve Defines a DER curve
mRID The global identifier of the curve
CurveData Contains the X/Y data pairs that define the curve shape
curveType 0 - Volt-VAr Mode
rampDecTms Defines the decreasing ramp rate limit
rampIncTms Defines the increasing ramp rate limit
xMultiplier Exponent for the X-axis values
yMultiplier Exponent for the Y-axis values
Frequency-Watt Curve Download
This function is intended to counteract frequency deviations by modifying real power output.
The inverter will adjust the inverter real power output based on the frequency at the point of
inverter connection using an X/Y curve. The X axis is the frequency and the Y axis is the
percentage of available real power output from the inverter. The SEP2 server provides the curves
to support this function. An example Frequency-Watt curve is shown in Figure 2-2.
Figure 2-2 Example Frequency-Watt curve with hysteresis
The Frequency-Watt function limits active power generation or consumption when the line
frequency deviates from nominal by a specified amount. The Frequency-Watt curve is specified
as an array of Frequency-Watt pairs that are interpolated into a piecewise linear function with
2-3
hysteresis. The x value of each pair specifies a frequency in Hz. The y value specifies a
corresponding active power output in percent of the inverter maximum real power output.
SEP2 Function set: DERCurve / DERCurveType: 1 - Frequency-Watt Curve Mode:
opModFreqWatt
Multiple curves may be supported to adapt to changing conditions. Some of the primary
elements of interest in this function are shown in Table 2-2. See the SEP 2.0 specification for full
details.
Table 2-2 Subset of the Frequency-Watt curve parameters
Structure Description
DERCurve Defines a DER curve
mRID The global identifier of the curve
CurveData Contains the X/Y data pairs that define the curve shape
curveType 1 - Frequency-Watt Curve Mode
rampDecTms Defines the decreasing ramp rate limit
rampIncTms Defines the increasing ramp rate limit
xMultiplier Exponent for the X-axis values
yMultiplier Exponent for the Y-axis values
Volt-Watt Curve Download
This function is intended to counteract voltage fluctuations on the feeder by modifying real
power output. The inverter will adjust the inverter real power output based on the voltage at the
point of inverter connection using an X/Y curve. The X axis is the voltage and the Y axis is the
percentage of available real power output from the inverter. The SEP2 server provides the curves
to support this function.
A simple Volt-Watt curve is shown in Figure 2-3.
2-4
Figure 2-3 Example Volt-Watt curve
The Volt-Watt function limits active power generation or consumption when the line voltage
exceeds nominal by a specified amount. The Volt-Watt curve is specified as an array of Volt-
Watt pairs that are interpolated into a piecewise linear function with hysteresis. The x value of
each pair specifies an AC RMS voltage. The y value specifies a corresponding active power
output in percent of the inverter maximum real power output.
SEP2 Function set: DERCurve / DERCurveType: 3 - Volt-Watt Curve Mode: opModVoltWatt
Multiple curves may be supported to adapt to changing conditions. Some of the primary
elements of interest in this function are shown in Table 2-3. See the SEP 2.0 specification for full
details.
Table 2-3 Subset of the Volt-Watt curve parameters
Structure Description
DERCurve Defines a DER curve
mRID The global identifier of the curve
CurveData Contains the X/Y data pairs that define the curve shape
curveType 3 - Volt-Watt Mode
rampDecTms Defines the decreasing ramp rate limit
rampIncTms Defines the increasing ramp rate limit
xMultiplier Exponent for the X-axis values
yMultiplier Exponent for the Y-axis values
2-5
DER Curve Enable/Disable
This function will activate a specific Volt-VAR, Frequency-Watt, or Voltage-Watt curve. The
curve enable uses the DERControl function from the SEP2 server. The DERControlBase
identifies the curve type to be enabled, and the DERCurveLink specifies the specific curve to be
enabled.
SEP2 Function set: DERControl / DERControlBase / DERCurveLink
When the event expires the DER curve function will be disabled. The event can also be
terminated at any time changing the duration.
Multiple curves may be supported to adapt to changing conditions. Some of the primary
elements of interest in this function are shown in Error! Reference source not found. See the
SEP 2.0 specification for full details.
Table 2-4 Subset of the DER curve enable/disable event structure
Structure Description
DERControl Defines a grid event
mRID Unique event identifier
interval The period during which the event applies
randomizeDuration Randomization time range to apply to the end of the
event
randomizeStart Randomization time range to apply to the beginning of
the event
DERControlBase Defines the event - opModFreqWatt, opModVoltVAr,
opModVoltWatt
A smooth transition from one curve to another is possible using SEP2. Implementing a different
curve does not require canceling the current event first before initiating a new event.
Ramp Rate Download
SEP2 DERControl events contain ramp rate parameters. These values must be provided to
manage the transitions from one setting to another.
Fixed Power Factor
This function is intended to provide a simple mechanism through which the power factor (PF) of
a DER may be set to a fixed value to generate or absorb reactive power.
2-6
SEP2 Function set: DERControl / DERControlBase: opModFixedPF
Refer to chapter 8, “Fixed Power Factor Function” in the EPRI Common Functions for Smart
Inverters report. Some of the primary elements of interest in this function are shown inError!
Reference source not found. See the SEP 2.0 specification for full details.
Table 2-5 Subset of the DERControl fixed power factor event structure
Structure Description
DERControl Defines a DER event
mRID Unique event identifier
interval The period during which the event applies.
randomizeDuration Randomization time range to apply to the end of the event
randomizeStart Randomization time range to apply to the beginning of the
event
DERControlBase Defines the event - opModFixedPF
opModFixedPF Fixed Power Factor Function
displacement Signed integer which translates to a value between -.9999
and 1.0000 defining the desired power factor
multiplier Specifies the exponent of the displacement.
Limit Maximum Real Power
This function is intended to provide a mechanism through which the maximum real power may
be limited to a percentage of the DER maximum real power.
SEP2 Function set: DERControl / DERControlBase: opModFixedW
2-7
Figure 2-4 Limit Maximum Real Power
Refer to chapter 4, “Maximum Generation Limit Function” in the EPRI Common Functions for
Smart Inverters report. Some of the primary elements of interest in this function are shown in
Error! Reference source not found. See the SEP 2.0 specification for full details.
Table 2-6 Subset of the DERControl limit maximum real power event structure
Structure Description
DERControl Defines a DER event
mRID Unique event identifier
interval The period during which the event applies.
randomizeDuration Randomization time range to apply to the end of the event
randomizeStart Randomization time range to apply to the beginning of the
event
DERControlBase Defines the event - opModFixedW
opModFixedW Limits real power output to this percentage of maximum
power output
2-8
Connect/Disconnect
This function is intended to provide a mechanism to connect or disconnect the DER from local
loads and the grid. While this is intended to be a physical disconnect, it is possible to imitate this
action on a DER without a disconnect switch by limiting the output to zero watts. This is not
considered a preferred solution for production units but is workable for purposes of a
demonstration. See Figure 2-5
DER Connect/Disconnect switch for a graphical description of the connect/disconnect switch.
Figure 2-5 DER Connect/Disconnect switch
For purposes of this demonstration, this will be the same as Limit Maximum Power to Zero
Watts. See the section above titled Limit Maximum Real Power for details on the
implementation.
Upload Inverter Alarms and Status
Reporting inverter status is performed using the MirrorMeterReading and DERStatus functions.
The SunSpec inverter interface provides values closely matched to the SEP2 DERStatus function
for operational state information. The meter mirroring can provide power, energy and power
factor values.
A method to report detailed alarm data has not yet been identified although DERStatus, but it
does return a single alarm state. This single alarm flag can be used for this demonstration and the
need for expanded alarm capability will be noted as a possible expansion to SEP2.
The data desired to be reported by the client is currently defined as:
Instantaneous real power
Instantaneous power factor
Totalized real power output
Connection status
Alarm flags
2-9
The alarm status should be configured to report on a minimum time schedule and on status
change.
3-1
3 IDENTIFIED ISSUES
One Event Active per Program
The SEP 2.0 specification calls out that a new event within a program supersedes the current
event within the same program, basically limiting all programs to a single event. Within the DER
control environment, it is expected to have multiple events active at the same time.
Ignoring these limitations can cause issues affecting inverter operation. For example, if a real
power limit is in effect and a Volt-VAR curve is then enabled, it may be impossible to modify
the real power limit since the server may consider that the event no longer exists.
Another issue is that a program may only have one default state, so the default state could not be
having a Volt-Watt curve enabled and a real power limit if both resided in the same program.
The solution to this is to place the functions in their own program, or in a program with mutually
exclusive functions. There appears to be no limitation on the number of programs that can run
simultaneously. This would allow multiple functions to be enabled at the same time with
multiple default states. This appears to be what was intended by the authors of the specification.